This is old, sorry if you have already figured this out.
I run lots of MADI through BNC patch bays. My understanding from the people at Digico and from other studio people using Euphonix is that you didn't want to get the ground plane / shield dirty and as such to use isolated bnc bulkhead connectors.
We have followed that practice religiously (whether we really need to or not I can't speculate on) and have never had a problem.
The MADI Bridge is helpful when you have to change patching (very) often. Such as dropping injest/playout systems in and out of line on a regular basis. It's also useful with it's optical ports to establish mid-range tie-lines between madi bridges if you have a purpose for that.
Karl P
